1. Technical Field of the Invention
The invention relates generally to communication systems; and, more particularly, it relates to communication devices that perform SOVA (Soft Output Viterbi Algorithm) decoding of signals within such communication systems.
2. Description of Related Art
Data communication systems have been under continual development for many years. One such type of communication system that has been of significant interest lately is a communication system that employs iterative error correction codes. Of those, one particular type of communication system that has received interest in recent years has been one which employs turbo codes (one type of iterative error correcting code). There are other types of iterative decoders in the art as well including those that employ LDPC (Low Density Parity Check) codes, as well as other types of codes. Communications systems with iterative codes are often able to achieve lower bit error rates (BER) than alternative codes for a given signal to noise ratio (SNR).
Within the context of many iterative type decoders, some of decoder implemented therein oftentimes employs a trellis to assist in the decoding of such signals. The typical prior art approach is to process one trellis stage (or trellis iteration) each clock cycle. One type of SISO (Soft-In Soft-Out) detector that can be employed within iterative decoding systems is a detector that performs decoding in accordance with the SOVA decoding approach. A main difference between a SOVA detector and a Viterbi detector is that while the Viterbi detector only outputs a hard decision, the SOVA detector outputs not only a hard decision but also a reliability (sometimes referred to as a ‘confidence’ of the hard decision) as well. This reliability information can be updated during subsequent decoding processing if desired as well.
A continual and primary directive in this area of development has been to try continually to lower the SNR required to achieve a given BER within a communication system. The ideal goal has been to try to reach Shannon's limit in a communication channel. Shannon's limit may be viewed as being the data rate to be used in a communication channel, having a particular SNR, that achieves error free transmission through the communication channel. In other words, the Shannon limit is the theoretical bound for channel capacity for a given modulation and code rate.
Generally speaking, within the context of communication systems that employ coding, there is a first communication device at one end of a communication channel with encoder capability and second communication device at the other end of the communication channel with decoder capability. In many instances, one or both of these two communication devices includes encoder and decoder capability (e.g., within a bi-directional communication system).